Effects of flaxseed lignan and oil on bone health of breast-tumor-bearing mice treated with or without tamoxifen.

Previous studies showed that flaxseed lignan (secoisolariciresinol diglucoside, SDG) and oil (FO) inhibit established breast tumor growth in athymic mice with or without tamoxifen (TAM) treatment. TAM was found to increase bone mineral content (BMC) and density (BMD) in breast cancer patients. It is not known whether SDG or FO alone or combined with TAM affects bone health. Hence, the effects of SDG and FO, alone or in combination, on BMC, BMD, and biomechanical bone strength in ovariectomized athymic mice with established human breast tumors (MCF-7) treated with or without TAM were studied. In a factorial design, mice were divided into four non-TAM and four TAM groups. Each group consisted of mice fed a basal diet (BD), SDG (1 g/kg), FO (38.5 g/kg) or SDG + FO (combination) diets. The TAM group had TAM implants that provide a 5-mg TAM dose released over 60 d. TAM exerted an overall significant effect in increasing BMC, BMD, and biomechanical strength in femurs and lumbar vertebra. Without TAM treatment, SDG produced significant lower femur BMD (6%) while FO produced lower vertebrae BMC (8%) and BMD (6%). With TAM treatment, SDG and FO did not exert an effect on BMC and BMD at the femur or vertebra. SDG and FO produced no marked effect on biomechanical bone strength with or without TAM treatment. In conclusion, FS components did not significantly attenuate the positive effects on bone induced by TAM in this model system, indicating no apparent adverse effects on bone health.